1. Field of the Invention
The invention relates to an X-ray examination apparatus comprising an X-ray source and an X-ray detector which are accommodated at some distance diametrically with respect to each other and can be rotated collectively about three axes relative to a table which can be moved between the X-ray source and the X-ray detector, which axes define a first system of coordinates and in which means are incorporated to determine a radiation vector along a central beam which connects the X-ray source and The X-ray detector, of which radiation vector a base is drawn by vectors situated along the axes of the first system of coordinates. Of interest is co-pending application Ser. No. 370,213, filed June 6, 1989, entitled "X-Ray Examination Apparatus Comprising Balanced Supporting Arm" in the name of Endschot et al and assigned to assignee of the present invention.
2. Description of the Prior Art
Such an X-ray examination apparatus is disclosed in U.S. No. 3,281,598. In an apparatus described in said specification the axes of rotation are realised by suspending the X-ray tube and the X-ray detector in a C-arm which is rotatable in the plane of the C-arm about a first axis. The C-arm is further connected to a support so as to be rotatable about a second axis, the support being connected to the ceiling so as to rotate about a vertical axis. The apparatus is isocentric, which means that the three axes have a common point of intersection, the isocentre. The isocentre customarily lies in an object to be examined.
The large freedom of movement of the system X-ray source-X-ray detector, hereinafter briefly referred to as the image-forming system, has many advantages. As a matter of fact, a patient can now be radiated under a great variety of directions. This is of great use, for example, for catheterisation.
German Patent Specification DE No. 21 08 657 discloses an X-ray examination apparatus in which a C-arm supports an X-ray source and an X-ray detector. Transducers to determine the position of the radiation vector are connected to the X-ray examination apparatus. By radiating an object in two mutually perpendicular directions, two projection images are obtained which are displayed on a television monitor, the signal values generated by the transducers which are also proportional to the angles of rotation of the C-arm being stored in a computing unit. An image line can be selected electronically in the two monitor images. A projection of the selected line can be computed for all the positions of the radiation vector which are measured by the transducers and be displayed in the X-ray image. For example surgery may take place along the selected line.
In use the known apparatus has as a disturbing drawback in that the orientation of a radiation image, for example, displayed on a monitor, rotates. The radiologist loses much time to be able to interpret the displayed image anatomically and the possibility of a wrong diagnosis increases. Further the freedom of movement of the operating personnel near a patient to be examined is strongly restricted.